The thing is, they just don't have that much control over the economy. I wish we could measure, or even estimate, the potential impact of a president with each issue. (I feel that given the breadth of political science, something like this should exists--I just haven't found it.) That way, people could judge candidates based on potential impact over all their issues of interest, instead of weighing a beast like the economy equally against things they have more control over, like healthcare and taxes.